curl --request PUT \
  --url https://app.pennylane.com/api/external/v2/transactions/{id} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "customer_id": 42
}'

{
  "id": 42,
  "label": "VIR SEPA MY SUPPLIER SAS",
  "attachment_required": true,
  "date": "2023-08-30",
  "outstanding_balance": "49.3",
  "created_at": "2023-08-30T10:08:08.146343Z",
  "updated_at": "2023-08-30T10:08:08.146343Z",
  "archived_at": "2023-08-30T10:08:08.146343Z",
  "currency": "EUR",
  "currency_amount": "120.00",
  "amount": "120.00",
  "currency_fee": "120.00",
  "fee": "120.00",
  "journal_id": 42,
  "journal": {
    "id": 234,
    "url": "https://app.pennylane.com/api/external/v2/journals/67"
  },
  "bank_account": {
    "id": 53,
    "url": "https://app.pennylane.com/api/external/v2/bank_accounts/53"
  },
  "pro_account_expense": {
    "employee": {
      "id": 42,
      "first_name": "John",
      "last_name": "Doe"
    },
    "card_masked_number": "123456XXXXXX7890"
  },
  "customer": {
    "id": 42,
    "url": "https://app.pennylane.com/api/external/v2/customers/42"
  },
  "supplier": {
    "id": 42,
    "url": "https://app.pennylane.com/api/external/v2/supplier/42"
  },
  "categories": [
    {
      "id": 421,
      "label": "HR - Salaries",
      "weight": "0.25",
      "category_group": {
        "id": 229
      },
      "analytical_code": "CODE123",
      "created_at": "2023-08-30T10:08:08.146343Z",
      "updated_at": "2023-08-30T10:08:08.146343Z"
    }
  ],
  "matched_invoices": {
    "url": "https://app.pennylane.com/api/external/v2/transactions/42/matched_invoices"
  }
}